Spectral analysis was used to identify periods in four academic library circulation series (journals, faculty books, student books, and turnstile count) and four of pickup for shelving (reference books, non-reference books, bound journals, and current journals).
Observed periods were compared to theoretical periods in a 364-day academic calendar: Two were expected, 182 and 7 days; one (122 days) was interpreted as a 112-day semester plus an interim of about 10 days; two were unexpected (3.5 and 2.3 days). The 182-day (about half an academic year) was strongest in the pickup series. The 7-day period was strong in all series. The 3.5 days was strong in most series. The 2.3 day, found only in circulation, is close to everyother-day usage or about 3 cycles per week, and may be due to Monday-Wednesday-Friday class scheduling, or it may be spurious. Only the 182-day period was visible in time charts. No evidence was found for a monthly period, the calendar unit in which library time series are often recorded.
Introduction-Periodicity
The cyclic nature of library use is familiar to all academic librarians. Reference activity peaks during certain hours and bottoms out at others. Days of the week, weeks of the semester, and semester of the year all have their highs and lows. Circulation coincides with class schedules and is heavy or light depending on the day. While other library activity (acquisitions, cataloging, processing) may or may not be cyclic, library managers still plan their days and weeks around the academic calendar.
Even so, understanding of these cycles is implicit, routine and experiential rather than explicit, systematic, or